Safety circuit for the detection of the simultaneous actuation of two antagonizing units

ABSTRACT

A safety circuit which is provided with two separate amplification channels, each of which comprises two cascadeconnected amplifiers. An approval signal is applied to a common input, and an approval signal can be derived from a common output if the units to be supervised function properly.

United States Patent [191 Boudault et al.

[451 Dec. 24, 1974 SAFETY CIRCUIT FOR THE DETECTION OF THE SIMULTANEOUSACTUATION OF TWO ANTAGONIZING UNITS 175] Inventors: Robert Boudault,Limours;

Christian Guion, 'Verrieres Le Buisson, both of France [73] Assignee:U.S. Philips Corporation, New

York, NY.

[22] Filed: Nov. 9, 1973 [21] Appl. No.: 414,377

[30] Foreign Application Priority Data Nov. 15, 1972 France 72.40508[52] US. Cl 315/130, 315/135, 340/41 R, 340/46, 340/78 [51] Int. Cl.H01j 7/42 [58] Field of Search .L 315/130, 131,135;

[56] References Cited UNITED STATES PATENTS 3,355,601 11/1967 Klein340/251 UX 3,457,430 7/1969 Samuelson 337/216 X Primary Examiner-HermanKarl Saalbach Assistant Examiner.lames B. Mullins Attorney, Agent, orFirmFrank R. Trifari [57] ABSTRACT I A safety circuit which is providedwith two separate amplification channels, each of which comprises twocascade-connected amplifiers. An approval signal is applied to a commoninput, and an approval signal can be derived from a common output if theunits to be supervised function properly.

2 Claims, 2 Drawing Figures Patented Dec. 24, 1974 2 Sheets-Sheet SAFETYCIRCUIT FOR THE DETECTION OF THE SIMULTANEOUS ACTUATION OF TWOANTAGONIZING UNITS The invention relates to a safety circuit for thedetection of the simultaneous actuation of two antagonizing units, eachof which is supplied with an alternating voltage via a static switch,the said circuit supplying an approval signal if no supply voltage issimultaneously applied to the two antagonizing units.

Antagonizing units are to be understood to means herein units which forreasons of safety may never be simultaneously active. For example, theseunits may be the green traffic lights which control the access ofvehicles to two intersecting roads, in which case the simultaneouslighting up of the two lights constitutes a major danger. Forcontrolling traffic lights, use is increasingly made of static powerswitches of the Triac type which are controlled by signals originatingfrom a control logic.

In spite of all precautions taken inthe choice and the use of theswitches and of the components of the control logic, certainty cannot beobtained that no internal faults will occur in the control logic or inthe switches (due to short-circuit or interruption of one or twojunctions of a Triac). These faults might cause the simultaneouslighting up of the green lights, the lighting up of a light beingcomplete or partial, depending on whether it is caused by one half-cycleor by both half-cycles of the alternating voltage.

The safety circuit has for its object to detect dangerous situations ofthis kind and to supply an approval signal if no voltage issimultaneously applied to the two lights, and to suppress this signal inthe opposite case. However, this circuit must be designed such that, nomatter what faults occur in its connections and/or components, theapproval signal is definitely suppressed if the status of the switchesgives rise to a dangerous situation.

The invention has for its object to provide a new structure for a safetycircuit of this kind for use when the antagonizing lights (and more ingeneral two antagonizing units) are supplied via static switches.

According to the invention, a safety circuit of this kind comprises twoamplification channels which receive an approval signal of a givenfrequency, the outputs thereof being coupled to the output of the safetycircuit, each amplification channel comprising a cascade-connection oftwo amplifiers, the direct current supply for these two amplificationchannels being provided for one of the amplification channels by a pairof supply circuits which are each connected to the terminals of theswitch which controls one of the antagonizing units, and for the otheramplification channel by another pair of supply circuits, each of whichis connected to the terminals of the switch which controls the otherunit, both supply circuits of each pair comprising a rectifier which isarranged in one supply circuit so as to rectify the positive half-cyclesof the alternating voltage and in the other supply circuit so as torectify the negative half-cycles, these two supply circuits supplyingthe one and the other amplifier of the amplification channel,respectively.

The invention will be described in detail hereinafter with reference tothe figures.

FIG. 1 shows the diagram of a safety circuit according to the invention.

FIG. 2 is a table showing the various states of the traffic lights andthe switches.

In FIG. 1 the safety circuit is used for the detection of thesimultaneous lighting up of two antagonizing green traffic lights at anintersection. These two lights L, and L are supplied by the alternatingvoltage between the supply lines 1 and 2 via the switches 8,, S(Triacs). The terminals 3, 4 of the switches 8,, S are connected to line1 via the lights L, and L The terminals 5 and 6 are connected to line 2.In this example,

the switches are Triacs, which means a switch which is made ofsemiconductor material in which pn-junctions are provided, the saidswitch being active for both positive and negative voltages and beingcontrollable at a control terminal. The switches 8,, S have control terminals 7, 8 which are connected to the logic unit 9 which controls thetraffic lights.

In the case of normal operation, logic unit 9 never supplies signalswhich cause the simultaneous lighting up of the two lights L, and LHowever, the latter situation may arise if given faults occur in thelogic unit. Faults can also occur in the switches 5,, S These faults(short-circuit or interruption) can occur in the one as well as in theother pn-junction or in both junctions at the same time. In the case offaults in the logic unit or in the switch, both lights L, and L canlight up simultaneously, a light being supplied by the positivehalfcycles or the negative half-cycles of the alternating voltage or byboth. In any case, the simultaneous lighting up of the two lights L, andL is considered danger ous. Y

The safety circuit detects all combinations of states of the switches S,and S which give rise to a dangerous situation. Between its two outputterminals 10 and 11 the safety circuit supplies an approval signal forthe status combinations which do not give rise to a dangerous situation,and it suppresses this signal for a dangerous situation. I i

The table of FIG. 2 illustrates all status combinations of the switchesS, and S In the first column the possible status combinations arenumbered from 1 to 16. The second and the third column relate to switch8,. Column A relates to the pn-junction which can be conducting duringthe positive half cycles of the alternating voltage, and the column Arelates to the pn-junction which can be conducting during the negativehalf-cycles. The symbols 1 and 0 in these columns indicate that therelevant pnjunction is conducting or non-conducting, respectively. Thefourth and the fifth column A; and A indicate in the same manner for theswitch S the states of the pn-junctions which can be conducting duringthe positive and the negative half-cycles, respectively. The columns L,and L, Show the states of the lights L,, L The symbol 0 indicates thatno voltage is applied to a light (extinguishing). The symbol 1 indicatesthat a voltage is applied to a light (lighting up). No distinction ismade between a voltage comprising positive and negative half-cycles anda voltage having only positive or only negative half-cycles. In the lastcolumn S the symbol 1 denotes a non-dangerous status combination forwhich the safety circuit must supply an approval signal, and the symbol0 denotes a dangerous status combination for which the safety circuitmust suppress the approval signal.

As is shown in the table of FIG. 2, the safety circuit must supply anapproval signal (S l) for the status combinations 1, 2, 7 in which atleast one of the two switches S and S is non-conducting for the positiveand/or the negative half-cycles of the alternating voltage. The approvalsignal must be suppressed (S for the status combinations 8, 9, 16 inwhich both switches are conducting.

According to the invention, the safety circuit shown in FIG. 1 comprisestwo amplification channels 12, 13, the input of which receives anapproval signal of a given frequency, the said signal always beingpresent between the terminals 14, 15. The outputs of the twoamplification channels 12, 13 are coupled to the output terminals 10, 11of the safety circuit via the transformer 16. The latter comprises twoprimary windings 17 and 18 which are connected to the output of theamplification channels 12 and 13, respectively, and a secondary winding19 which is connected to the terminals 10, 11. Each amplificationchannel 12, 13 comprises two amplifiers 20 and 21, 22 and 23,respectively, which are cascade-connected and which are coupled via atransformer 24, 25. The direct current supply for the amplificationchannel 12 is provided by the supply circuits 26, 27, the inputs ofwhich are connected parallel to the terminals 3, of the switch 8,(directly for the terminal 3, and by way of the resistor 28, 29 for theterminal 5). The direct current supply for the amplification channel 13is provided by the supply circuits 30, 31, the inputs of which areconnected parallel to the terminals'4, 6 of the switch S (directly forthe terminal 4, and by way of the resistor 28, 29, for the terminal 6).Each of the supply circuits 26, 27 comprises a rectifier 32, 33,respectively. The rectifier 32 of the circuit 26 is connected so as torectify the positive half-cycles of the alternating voltage, and therectifier 33 of the circuit 27 is connected so as to rectify thenegative halfcycles. Each ofthe supply circuits 30, 31 comprises arectifier 34, 35, respectively. The rectifier 34 of the circuit 30 isconnected so as to rectify the positive halfcycles of the alternatingvoltage, and the rectifier 35 of the circuit 31 is connected was torectify the negative half-cycles. In the supply circuits 26, 27, 30, 31the rectifiers 32, 33, 34, 35, respectively, are connected to asmoothing circuit which consists of the parallel connection of a Zenerdiode 36, 37, 38, 39 and a capacitor 40, 41, 42, 43, respectively. Thedirect voltages which are obtained on the outputs of the supply circuits26, 27 are applied to the input terminals of the amplifier 20, 21,respectively, of the amplification channel 12. Similarly, the directvoltages obtained on the outputs of the supply circuits 30, 31 areapplied to the input terminals of the amplifier 22, 23, respectively, ofthe amplification channel 13.

In the safety circuit the'supply circuits 26, 27, 30 and 31 perform thefunction of detectors of the status of the switches S, and S The twoamplification channels 12 and 13 perform the function of a logic circuitwhich allows passage of the approval signal or blocks this signal inaccordance with the table of FIG. 2.

This is because the supply circuit 26 applies a supply voltage to theamplifier only if an alternating voltage containing positive half-cyclesis present on the input,

i.e. when switch S is not conducting during the positive half-cycles.The supply circuit 27 applies a supply voltage to the amplifier 21 onlywhen the switch S is not conducting during the negative half-cycles. Inthe same manner, the supply circuits and 31 apply a supply voltage tothe amplifier 22, 23 only if the switch S is not conducting during thepositive or negative halfcycles, respectively, of the alternatingvoltage.

In the status combinations 1, 2, 7 according to the table of FIG. 2, atleast one of the switches S and S is not conducting for the positiveand/or negative halfcycles, with the result that the amplifiers of atleast one amplification channel 12 or 13 receive their supply voltage.The approval signal which is applied to the input terminals 14, 15 ofthe safety circuit then reaches the output terminals 10, 11.

In the status combinations 8, 9, 16 of the table of FIG. 2, bothswitches S and S are conducting during at least one of the twohalf-cycles of the alternating voltage, with the result that at leastone of the amplifiers of the two amplification channels 12 and 13receives no supply voltage. In this case the two amplification channels12 and 13 are blocked, with the result that the approval signal issuppressed.

The safety circuit shown in FIG. 1 optimally satisfies the safety rulethat faults in the connections or components can cause the suppression.of the approval signal, but in any case prevent that the suppressiondoes not take place in one of the dangerous status combinations 8, 9,16. In general it is assumed that the component faults to be taken intoconsideration are a short-circuit or an interruption for thepn-junctions and the capacitors, and an interruption for the resistorsand windings of the transformers.

The two amplification channels 12, 13 between the input l4, l5 and theoutput 10, 11 of the safety circuit are constructed in conformity withthe said safety rule.

Each of the amplifiers can be constructed as shown in FIG. 1 foramplifier 20. This amplifier comprises a transistor 44, the base ofwhich is connected to the input terminal 15 by way of the resistor 45,its emitter being connected to the input terminal 14 and to'the supplyterminal and its collector being connected to the supply terminal by wayof the resistor 46 and the primary winding of the transformer 24. Theresistor 45 limits the current at the input of the amplifier 20, withthe result that in the case of a fault in this transistor the approvalsignal is substantially not applied to the amplifier'21. The resistor46limits the collector current of the transistor 44. Connected betweenthe terminals of the primary winding of the transformer 24 is the diode47 in order to eliminate overvoltages which might damage the transistor44. A fault in one of the components of the amplifier 20 causessuppression of the approval signal in the amplification channel. Theapproval signal on the output terminals 10, 1 1 is then immediatelysuppressed if the light:l. is on or will be interrupted as soon as thelight L is switched on.

The supply circuits 26, 27 and 30, 31 are also constructed in conformitywith the said safety rule. In'the case of an interruption or ashort-circuit of the rectifier 32 of the supply circuit 26 or ashort-circuit of the capacitor 40 or of the Zener diode 36, theamplifier 20 is no longer supplied with a voltage and the approvalsignal is suppressed in the amplification channel 12. In the case ofinterruption of the Zener diode 36 or of the capacitor 40, the amplifier20 is not normally supplied and can possibly function, but in that casethe supply circuit 26 continues to perform its function as detector ofthe status of switch S The approval signal which is applied to the inputof the safety circuit may be a sinusoidal alternating voltage, but canalternatively be a pulse-shaped signal.

For an intersection comprising a plurality of pairs of antagonizingtraffic lights, the number of safety circuits equals the number of saidpairs. It will then be advantageous from a safety point of view toconnect these safety circuits in cascade so as to form one safety unitcomprising one input and one output for the approval signal.

What is claimed is:

l. A safety circuit for the detection of the simultaneous actuation oftwo antagonizing units, each of which is supplied with an alternatingvoltage via a static switch, said safety circuit supplying an approvalsignal if no supply voltage is simultaneously applied to theantagonizing units, characterized in that it comprises two amplificationchannels which receive an approval signal of a given frequency, theoutputs thereof being coupled to the output of the safety circuit, eachamplification channel comprising a cascade-connection of two amplifiers,the direct current supply for these two amplification channels beingprovided for one of the amplification channels by a pair of supplycircuits which are each connected to the terminals of the switch whichcontrols one of the antagonizing units, and for the other amplificationchannel by another pair of supply circuits, each of which is connectedto the terminals of the switch which controls the other antagonizingunit, both supply circuits of each pair comprising a rectifier which isarranged in one supply circuit so as to rectify the positive half-cyclesof the alternating voltage andin the other supply circuit so as torectify the negative halfcycles, these two supply circuits supplying theone and the other amplifier of the amplification channel, respectively.

2. A circuit as claimed in claim 1, characterizedin that each amplifiercomprises a transistor, the base of which is connected to an inputterminal of the amplifier, its emitter being connected to the otherinput terminal of the amplifier and to a supply circuit output terminal,andits collector being connected to the other supply circuit outputterminal by way of a primary winding of a coupling transformer.

1. A safety circuit for the detection of the simultaneous actuation oftwo antagonizing units, each of which is supplied with an alternatingvoltage via a static switch, said safety circuit supplying an approvAlsignal if no supply voltage is simultaneously applied to theantagonizing units, characterized in that it comprises two amplificationchannels which receive an approval signal of a given frequency, theoutputs thereof being coupled to the output of the safety circuit, eachamplification channel comprising a cascade-connection of two amplifiers,the direct current supply for these two amplification channels beingprovided for one of the amplification channels by a pair of supplycircuits which are each connected to the terminals of the switch whichcontrols one of the antagonizing units, and for the other amplificationchannel by another pair of supply circuits, each of which is connectedto the terminals of the switch which controls the other antagonizingunit, both supply circuits of each pair comprising a rectifier which isarranged in one supply circuit so as to rectify the positive half-cyclesof the alternating voltage and in the other supply circuit so as torectify the negative half-cycles, these two supply circuits supplyingthe one and the other amplifier of the amplification channel,respectively.
 2. A circuit as claimed in claim 1, characterized in thateach amplifier comprises a transistor, the base of which is connected toan input terminal of the amplifier, its emitter being connected to theother input terminal of the amplifier and to a supply circuit outputterminal, and its collector being connected to the other supply circuitoutput terminal by way of a primary winding of a coupling transformer.